How Do Car Batteries Work?

Written on November 25, 2015 at 9:54 pm

Provided it works, a car battery is something that most motorists take for granted. With a high quality battery such as those supplied by Manbat, we’d like to think that you will experience years of reliability. This does of course rely on properly looking after both battery and vehicle to ensure maximum efficiency in the electrical and charging systems.

Whilst we all know what a battery is for and most people have a basic understanding of how they are charged, something that is less well known is this: How does a car battery actually work?

Basic Structure

The first thing to understand is that unlike the batteries typically used for electronic devices such as remote controls and clocks, a car battery is actually 6 smaller batteries that are lined up in series. This causes the voltages of each battery to add, giving the total voltage. In the case of a car battery, this is usually 12 volts (although in actual fact the true voltage is 12.6). A wide range of other vehicles use the same battery technology in a range of voltages, however the principle remains the same.

What Happens Inside

The general way that a battery works is that when an electronic circuit is connected to the battery, electrons are allowed to flow. For the scientific minded, an electron is a subatomic particle, (symbol e− or β−), with a negative elementary electric charge. It is the electrons that play the all important role of providing power.

Inside the battery are 3 important things. There are 2 connectors that go out of the battery, known as the cathode and anode. There is also a solution that the cathode and anode sit in. During normal operation, a chemical reaction occurs between the solution and the anode which releases electrons that flow through the circuit. These re-enter the battery through the cathode where another chemical reaction is happening between the cathode and solution. The electrons are incorporated in the products of this reaction. When run in reverse (with certain batteries), electrons are forced in the other direction in the reverse reactions. When a battery dies, it is usually because one or more of the chemical reactants is more or less used up.

The Chemistry of Batteries

In a car battery (often known as a lead-acid battery) the cathode is lead dioxide (PbO2), the anode is a sponge of lead (Pb), and the solution is sulfuric acid (H2SO4). When the battery is being used, the 2 connections react to form lead sulfate (PbSO4) by reacting with the sulfuric acid.

Specifically, the two reactions are:

PbO2 + 4H+ + SO4— + 2e– -> PbSO4 + 2H2O and

Pb + SO4— -> PbSO4 + 2e–

Notice that one reaction releases electrons and the other uses them up. Since the electrons can’t travel directly through the solution to get from where they’re released to where they’re used, the reactions can only continue if they travel through the external electrical circuit.

Recharging

The reverse reaction happens when the battery is being recharged. This reaction produces roughly 2V. The 6 cells add to give the 12V necessary to start a car. It is this reverse reaction that allows batteries to be used over and over again.

At Manbat, we take pride in providing the highest quality batteries as well as exceptional after sales support. A wide range of technical information including spec sheets and technical information for battery fitters is available from our website.